Debbie Jevans has resigned as chief executive of the organising committee of this year's Rugby World Cup, citing "personal reasons".
Jevans, who was previously director of Olympic sport for the London 2012 Games, has been in charge of England Rugby 2015 since October 2012.
A statement from England 2015 said: "Debbie Jevans CBE has decided to resign as chief executive of England Rugby 2015 (ER2015) due to personal reasons.
"Debbie has been at the helm of the Rugby World Cup Organising Committee since October 2012, and leaves with a highly experienced event delivery executive team in place, with plans for the tournament in excellent shape. All aspects of tournament preparations are on or ahead of schedule, with over 1.9 million tickets sold to date."
Jevans said: "This is the right decision for me to make at this time. I am immensely proud of the team and all that we have achieved in the time that I have been chief executive.
"Everything is in place to ensure that this is the best Rugby World Cup ever, and I am confident my team will deliver an exceptional tournament.
"The organisation is strong, there is a great team in place and I am really looking forward to watching the Rugby World Cup as a fan later this year."
Stephen Brown, the Rugby Football Union's financial director, will take over Jevans' responsibilities and has been appointed managing director.
England Rugby 2015 chairman Andy Cosslett said: "On behalf of the ER2015 Board I would like to extend our enormous appreciation for all that Debbie has brought to the role.
"Her legacy will be seen during and after the tournament is delivered, with a sporting event that I fully believe will be both memorable and inspiring, creating a step change in interest and participation for the game in this country."
World Rugby chairman Bernard Lapasset added: "On behalf of World Rugby I would like to thank Debbie for her vision, dedication and leadership in implementing everything we need for an exceptional Rugby World Cup and wish her all the best for the future. We are confident that Rugby World Cup 2015 will be the biggest and best to date."
Jevans' departure comes just 24 hours after she welcomed confirmation of 15 Rugby World Cup fanzones to be installed for the tournament this autumn.
More than one million people are expected to attend the fanzones, which will feature big screens and entertainment in all the host cities.
Organisers also announced the Rugby World Cup trophy tour in the UK and Ireland, which begins on June 10.
Jevans said on Thursday: ''The countdown to Rugby World Cup 2015 is on and fans can now really begin to plan their tournament experience, be it through watching the matches, through fanzones, the festival of rugby and the Rugby World Cup trophy tour.
''Capacities will range from 2,000 to over 10,000 and we would like to thank all of our host cities, local authorities and the Mayor of London for their fantastic support and we look forward to welcoming upwards of one million people to the official fanzones.
''The Rugby World Cup trophy tour will be the perfect opportunity to excite and engage fans across the UK and Ireland and make 2015 feel like the year of the rugby nation.
''Delivering a continuous 100 day tour means we can give as many fans as possible the opportunity to see the Webb Ellis Cup.''